don't waste your time with the holga lens for your d50. if you really want one, holgamods dude makes and sells 'em but the image quality is worse than ****. dab some vaseline on your cameraphone and you've got a dslr + holga lens. if you're gonna play around with homemade lenses, i'd highly suggest the DIY lens baby (medium format lens + plastic bellows) or attempt the ultimate hipster camera: the digital lomo l-ca.

i've seen some pretty neat riggings for both digital holgas and the single digital l-ca i believe exists. the dholga actually projected onto a piece of frosted glass which was placed squarely in front of a p&s camera - so it was actually more of a digital holgabscura. the digital l-ca was in fact an epson r-d1 with a custom machined lens housing which held the main lens element from a wrecked l-ca. i'm told the results are quite nice.